The present application relates to systems and methods for fabricating composites.
Composites have a variety of applications in a broad range of industries, such as aircraft manufacturing, boat hull fabrication, automobile body fabrication, as well as others. The fabrication of a composite often involves formulation of individual composite parts and the alignment and bonding together of those composite parts into a composite assembly. During this fabrication process, the composite is subjected to a number of high temperature curing and bonding operations. Alignment tolerances between the composite parts during the bonding operations can be narrow, for example, on the order of about 0.005 inch. Maintaining proper alignment within such narrow tolerances can be difficult due to thermal expansion and contraction of the composite parts and the tooling apparatus used to form the parts. This is because thermal expansion may cause movement of the composite parts relative to one another and/or the tooling apparatus during the thermal cycles of the bonding and curing operations. The problem is exacerbated where the parts and/or the tooling apparatuses are made from materials having differing coefficients of thermal expansion (CTE), which cause the parts and/or tooling apparatus to expand and contract at different rates.
Failure to maintain alignment within the desired tolerances can cause undesirable structural defects, such as voids or stress risers in the bond lines of the composite parts. These defects may require repair or scrapping of the composite parts altogether, which can be costly.
In the past, the problem of maintaining proper alignment of composite parts of an assembly during thermal processing has been dealt with by installing slotted bushings in the surface of the tooling apparatus used to fabricate the assembly. The composite parts are held in place on the surface of the tooling apparatus using pins inserted into the slots of the bushings. The pins are attached to the composite parts by either cutting mating holes in the wet composite parts through which the pins can be inserted and then curing the pins directly into the composite parts, or by installing transfer pins in the bushings and then back-drilling the hole in the composite part after it is cured. The pins attached to the composite parts move back and forth in the bushings to allow for thermal expansion and contraction of the composite parts during processing.
However, there are certain problems with the above-described methods. For example, the slots in the bushings often fill with resin, which is used to form the composites, and become useless. In cases where back-drilling is employed, the resulting holes in the composites are not always positioned accurately. Further, during multi-step bonding operations, the pins bear upon the sidewalls of the holes in the composites, often causing the mating holes by which the pins are held in the composite parts to become oversized. The oversized mating holes may allow the pins to become improperly positioned in the composite parts, which may result in failure to maintain the proper tolerances for producing an acceptable composite assembly.